1. Field of the Invention
This invention relates in general to well pumps of a progressive cavity type using a downhole electric motor, and in particular to a flexible connector for connecting the rotor of a progressive cavity pump to the drive shaft of the motor.
2. Description of the Prior Art
A progressive cavity pump is a type of pump that has a helical metal rotor that is rotated within an 11 elastomeric stator that has double helical cavities. Rotating the rotor forces the liquid from an intake end to an output end.
The rotor will rotate in an eccentric or orbiting motion. This complicates the means for driving the rotor. In one type of assembly, a downhole electric motor is installed with the pump. Electrical power is supplied to the motor for rotating the pump. The motor has a drive shaft that rotates on an axis, not eccentrically. Various connector assemblies have been devised to accommodate the orbiting movement of the lower end of the rotor. One type employs U-joints on ends of a connector shaft. The U-joints allow the rotor end to orbit while the drive shaft end remains on the axis. The connector shaft remain straight and inflexible during operation. While workable, U-joints wear.
In this invention, a connector assembly is provided for a progressive cavity pump that uses a connector shaft that flexes. The rotor end and the drive shaft end of the connector shaft are splined. A rotor coupling connects the splined rotary end to the connector shaft. A drive shaft coupling connects the splined drive shaft end to the drive shaft. A guide bushing restrains the drive shaft coupling from orbiting. The shaft is a solid metal member, such of as steel. Its length and diameter are selected so that it will flex and accommodate the orbiting movement of its rotary end. The length and diameter is also selected so that the downthrust transmitted along the shaft to a thrust bearing in a seal section below the connector will not cause the shaft to buckle.